You can’t book a table. You will find a card with your allocated table number in your stateroom on arrival. If you mean Cunard fare you can choose the early or late slot for fixed dining but you can only express a preference for table size. Freedom dining means you don’t have a fixed time slot, table or table size. You just arrive at the restaurant at a time of your choice but you may have to wait to be seated at busy times. You can check if your table table / time suits you on embarkation day usually after 1 30 and ask to move if it’s not suitable providing there is an alternative option available.